Phos-Zorb is a special filtration material great for use in many applications, including canister filters and wet/dry filters & sumps. Phos-Zorb selectively removes phosphate and silicate. Phosphate is a by-product of fish metabolism, decaying organic matter, and is an additive in some water conditioners and filter medias. In saltwater aquariums, excess phosphate lowers the available calcium and magnesium necessary for the growth of hard corals and other invertebrates. Excess phosphates also promotes the growth of unwanted nuisance algae, and can lead to poor coral health and bleaching. Silicates promote the growth of unwanted brown diatom films.